Duty's first transformation preceded the markers of disease. Since Mercymorn cured him and gave him a clean bill of health, he has continued to dive to no ill effect. Turning into a squid is not only a curse, it's their natural state as witnessed by their death and rebirth process, as evidenced by their arrival. Only this disease is something more, something akin to beasthood, something in their blood and bodies.

"Spike of adrenaline," he states calmly. "While deep underwater." Out in the ocean, the place he has naturally twice returned to full squiddom without death and once with. He's grown more comfortable with the reality that they are all squids, no matter how they dress themselves up.